Unlike DSC, which measures the overlap of volumes, the NSD measures the overlap of two mask borders [1]}. The metric uses a threshold that is related to the inter-rater variability of the annotators. According to [2]}, their calculations resulted in a threshold of \(\tau := 13\)  for the challenge's data set. To calculate the MI_DSC and MI_NSD, matches of instrument instances were computed. Then, the resulting metric scores per instrument instance per image were aggregated by the mean.
